Transmitter and receiver



Oct'. 2, 1934. c. w.jHANsE|.L. 1,975,270

TRANSMITTER AND RECEIVER Filed April a.' 1930 0? INVENTOR C W. HANSELL.

+ g h.. BY MTQRNEY the signal frequency.

4plitude is low when wg STATES PATENT OFFCE TRANSMITTER AND RECEIVER Clarence Weston Hanseil, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware a' Application April 8, 1930, Serial No. 442,554

6 Claims.

This invention relates to radio apparatus and in particular to complete radio stations including transmitting apparatus and receiving apparatus.

An object of the present invention is to provide means through lwhich the amplitude of the carrier frequency generated for transmission is controlled in accordance with theamplitude of the modulating frequency.

A further object of the present invention is to l provide means associated with the signal modulating means and the 'carrier frequency generating means in the transmitter by which the amplitude of the carrier frequency generated is automatically controlled in accordance Wtih'the aml plitude of the modulating frequency applied to the carrier frequency. i

An additional object of the present invention is to provide means whereby the amplification factor of the receiver bears a definite predetermined ratio with respect to the amplitude of the modulating frequency in the transmitter.

A further object of the present invention is to provide means associated with the modulation frequency amplifier in the transmitter and with -the radio frequency amplifiers in'the receiver,

whereby the amplification factor of the kampliners rin the receiver is automatically determined by the amplitude of 'the modulating frequency in the modulation frequency amplier in the.

transmitter.

Another object of the present invention is to provide a novel transmitter and receiver in com.

bination with novel control apparatus as briey described above in which the Weight of the entire ,apparatus is kept lowl bythe elimination of the.

heretofore necessary heavy apparatus, as for instance choke coils having large iron cores, transformers, large power sources, etc.

Briefly, the first two objects are attained by the use of a biasing resistance in the grid-cathode circuit of the modulation y'frequency amplifier which is arranged to give self rectication of the signal frequency, `in such a manner as to control the resistance of the anode cathode circuit of the modulation amplifier, thereby controlling the average potential applied from theanode of the modulation frequency amplifier to the element in the carrier frequencygenerator through which the carrier frequency is modulated in accordance with This automatically controls the amplitude of the carrier generated.

An obvious advantage resulting from this arrangement is that there is a great saving in en-` ergizing current since the carrier frequency amthe operator-is not speakingl (Cl. Z50-9) and increases proportionately to the increase in amplitude of the modulating frequency impressed by the operator. This results directly in a reduction in size of the power sources necessary to energize the apparatus, and it is extremely inipor. tant the weight of apparatus of this nature be kept as low as possible.

The second listed objects are attained by utilizing the potential fall in the resistance in the control electrode-cathode circuit of the modulation frequency amplier referred to above to determine the potential of a control grid in the receiver or of the control grids in a tube or in tubes of theA radio frequency amplifier circuits therein in, such a manner as to prevent the radio frequency amplifiers from amplifying when the operator is speaking into the modulationfrequency amplifier in the transmitter, and to insure that the receiver or the radio frequency amplifiers therein is or are highly responsive to signals received on the receiver antenna, when the operator is not speaking.

One advantage to be gained by the use of con-v trol apparatus of the nature described is that notv only is the receiver rendered inoperative when the operator is speaking into the transmitter, but signals from the transmitter are prevented from reflecting back to the receiver and reaching the operator. Y

Numerous other advantages will become appar-- ent from the reading of the following detailed description and therefrom when reading in con-f` nection with the attached drawing.

The invention may be used with any transmitter' or receiver known heretofore but is particu-- larly applicable to transmitters of the type disclosed in C. W. Hansell U. S. application No. 424,- 761, vfiled January 31, 1930. i

The nature of the invention and the, operation` and utilitythereof will be better understood by' reference to the single figure in the drawing in which' for purposes of illustration a transmitter T` is shown at the left of the dotted line and a radio receiver R shown at the right of the dotted line. It will be understood that the radio receiver and transmittershown are merely shown for purposes of illustration since applicants novel method of and apparatus for controlling the amplitude of the carrier frequency generated in accordance with the amplitude of the modulating frequencyl and method of and apparatus for automatically cutting 'off and on the receiver used, may be applied to other transmitters, as for instance, a transmitter of the type shown in copending application No. 424,761 filed January 31, 1930, and. to any receiver in general use today, without departing from the spirit of the present invention.

In the drawing, 1 indicates a thermionic oscillation generator, and 2 a modulation amplierf Anode potential is supplied to thermionic oscillation generator l through tankY circuit 3 from a i generator, and from the same source 4 to the anode 5 of therrnionic modulation ampliier 2 through a charging resistance 7. The anode cathode direct current circuits of the amplier l2 and oscillation generator 1 arecompleted through bus bar 9 connected to the lamentsV 10 and 11 of thermionic tubes 2 and 1 respectively. Current from the source '1- is smoothed by means of a series induc'tance 14 and parallel condensers C1, C2 connected between the source 4 and the electrodes of thermionic tubes 2 and 1. The tank circuit VV3 connected between the anode 6V and cathode 11 of thermionic oscillation generator 1 includes an inductance 15 tuned to the desired frequency by a variable condenser 16. This tank circuit may be associated; with any type of antenna, as for instance, the doublet 17 coupled through inductance 18 to the inductance 15 in the tank circuit. The frequency of` the carrier Wave generated in oscillation generator 1 is further controlled by a long line frequency control somewhat similar to the control disclosed in detail in James L. Finch et al. Patent No, 1,915,545, which issued upon United States application No. 353,660 led May. 16, 1929. is connected through a blocking condenser 2O to the ygrid 21 of the oscillation generator at one end and capacitively coupled to the aerial inductance 18 at the other end. The inductance 18 is coupled yto the inductance 15 in the anode circuit of the thermionic oscillation generator 1.

As set forth in detail in application No. 363,660, filed May 1'6, 1929 if the line connecting the anode to the `control electrode is made equivalent to an.

odd number of half wave lengths a potential variation on the anode will cause a corresponding potential change on the control electrode. There will be an 180 phase difference between said This results in regeneration at theA i thellline between the electrodes, the phase change in anycondensers or inductive couplings in series with the line must be taken in consideration. As for example, in the present long line control, the line includes the Vcondenser 20, lead 19, capacitive coupling between the terminal of 19 and inductance 18 and the coupling between 18 and 15. The sum total of the electrical length of this line should equal an odd number of half wavelengths to #properly control the frequency of ythe oscilla'- tio'ns-generated. The tube capacity of thermionic generator 1 is tuned by means of a variometer 23 to give la resistive termination at the end'of line 19 which shouldpreferably be equivalent to the characteristic vor surge resistance of line 19, so

. that the phase of -radio frequency anode and controlelec'tro'de voltage will be correct for the most.

eilicie'nt oscillation of thermionic generator 1. Biasingvpotential is obtained for the control :grid oftliermionic oscillation generator 1 by using the potential drop in current, obtained` by grid rectic'ation, through a grid leak resistance R Vcon'- nected through a reactance ora second resistance nl. between 'the iament 11 and Control 'grid 21 df ftherrnionic Aoscillation generator 1. The re'- V:iistance R1 or reactance is of such a valueasto The long line frequency control 19 prevent short circuiting of the radio frequency in the control electrode cathode circuit through the by-pass condenser 26Aconneoted in parallel with resistance R. j' The biasing resistance R biases the control grid 21 of thermionic oscillation generator 1 to a point most suitable for oscillation genera tion.

The high frequency oscillations generated in thermionic generator 1 are modulated at voice frequency through the shield grid Y27 which is connected to the anode 5 of modulation amplier 2. Voice frequencies are impressed on the electrodes 28, 10 of modulation frequency amplier 2 by means of the secondary winding 29 of a transformer 30 having its primary winding 31 connected to a microphone M. The secondary Winding 29 of said transformer is connected through a biasing resistance R2 between the control grid 28 and lament 10 of amplifier 2. Alternating currents in the control electrode cathode circuit of the ampliiier 2 are shunted around resistance R2 by means of a condenser 34. The resistance R2 is of such a value asto maintain the control electrode 28 of amplifier 2v at zero potential when the operator is not speaking. When the potential of theA control electrode 28 of thermion-ic tube 2 is zero thermionic tube 2 has a low anode cathode space resistance. This-resultsin a l'ow potential being applied to the -screen gridV of the thermionic oscillation genera-tor 1 and maintains the output of the oscillation generator 1 at Zero or at a low value. When the operatorspeaksA into the microphone thereby. impressing modulating frequencies on the kcontrol electrode 28 of amplifierZ the grid rectificationA action in amplifier 2: causes `a direct current to flow through theresistance Rz. The potential ldrop through R2 is applied tothe control eleotrode 'of tube 2 impressing thereon ay potential relative lto the 4cathode of, 2 which is proportional to the strengthyof the `modulation frequency impressed on the input circuit of 2. This steady biasr raises the average screen grid potentie-lofi the oscillation generator 1 and causes a carrier4 waventobe transmitted which is modu lated by the 'voice of the operator. At the same time-this biasing :potential set up across R2 serves as ra control lfor the `amplification -of the radio receiver which lis shown at the right of the single iigure` and which will `new fbe described.

The radio receiver which is shown lmerely for purposes fof illustration-includes an aerial -50 connected through-an inductance A5-1 to thebus bar 90. The inductance 5:1 forms the primaryof a transformer having 'a-secon'dary winding 52 connected` between the controlvgrid 53V and cathode 5e` of the iirst radiov frequency amplifier 56.

Means for preventing `'electrical disturbances in.

aerial from reaching `the secondarywinding 52 isprovided in the formof an electrostatic screen 55 located between primary winding 51 and secondaryA winding 52, -thescreen 55 being grounded to vthefbus-bar -90, The output circuit of. the'amplier 5 6includeslan inductance 5'? tuned by means of a Econdenser A58 l connected through a resistance '60 yand the 4power-source 4` between the anode 59- and cathode 54 ofthe amplifier 56. The resistancel 60 'in series with the power source 4 reduces `theyoltage toa value whichl is applicable to the-:anodes of thetubesusedas-the radio frequency amplifiers.

to the control electrode A'of a second radio .frequency amplifier 63. A'Ihisamplier 63 lis similar to the .prior amplier ljust 'discussed and further description thereof -isithouglit unnecessary except The anode-590i ampliiier 56 is 'connected through af coupling 'condenser -6l to note that the control lelectrode of the radio frequency amplifier- 63 is supplied with biasing potential through an impedance 62 whereas the control electrodey of the amplifier 56 is supplied with biasing potential through the secondary winding 52 of the transformer.

To prevent the voltage of the` source 4 from rising to a value injurious to the current smoothing device or to the thermionic tubes when the oscillation generator 1 and amplifier 2 are ,inoperative a resistance 68 is connected across the direct current line as shown, one terminal of the resistance being connected to the low voltage end of the resistance 60. Any radio` frequencies present in the source 4 due to the oscillation in generator 2 are shunted around the resistance 68 by means of condenser 69.

The radio receiver may have'several stages similar to the stages described above and the radio frequency amplifier stages may feed into any known form of detector.

The control electrode cathode circuit of each of the radio frequency amplifiers in the radio receiver is completed through a potential source 64, lead 65, resistance R2 ofv .theftransmitter and thence through bus bar 9 and 90 to the cathodes of the respective receiver amplifier tubes.

The specific radio receiverand detector forms no part ofthe present invention andv illustrations thereof other than as given aboverare thought unnecessary.

The input winding 52 of the amplifier 56 and the inductance 62 of the amplifier 63, connected to the control grids of the radio frequency amplifier 56 and 63 respectively, are connected through a biasing battery 64 to the terminal of resistance R2 described above in connection with the description of the transmitter T for a purpose which will now be set forth.

When the oscillation generator 1 is not being modulated at voice frequencies the potential of the grid of the oscillation generator 1 is maintained at Zero and little or no carrier frequency is transmitted. The potential drop across the resistance R2 is small and the battery 64 applies to the control electrodes of the radio frequency amplifiers 56 and 61 respectively, a negative potential such that the amplification factor of each of the amplifiers in the receiver is high and signals are received in the radio receiver.

When the Aoperator speaks the Voice modulation currents flowing in the control grid cathode circuit of the modulation amplifier 2 causes a relatively heavy direct current to flow through resistance R2 thereby causing a potential drop through R2. This potential drop is added to the potential applied by 64 to the control electrodes of the amplifiers in the radio receiver, and maintains said electrodes at a negative potential with respect to their cathodes to prevent reception of signals in said receiver. In other words, by applicants novel arrangement the control electrodes of the radio frequency amplifiers are maintained at such a value that signals are not received while the operator is speaking but are received when the operator is not speaking.

To repeat briefiy the operation of applicants novel combination of transmitter, receiver and automatic control means therefor, assume the operator is not speaking into the microphone, no

' current is flowing in R2 the control electrode of the modulation frequency amplifier is at or near zero potential, the amplifier has low anode cathode resistance, the screen grid of the oscillation y generator is at low potential and little or no carrier frequency oscillations appear in the output circuit thereof.

The receiver amplifiers are biased only by battery 64 and are sensitive to signals.

The operator now speaks into the microphone. Current flows in R2 the bias on the control grid of the modulation frequency amplifier changes. TheA potential applied to the screen grid of the carrier `frequency generator increases-carrier frequency oscillations are generated and radiated from the antenna circuit. Simultaneously a negative potential equal to the potential drop through AR2 is added to the negative potential applied by the biasing battery 64k to the control velectrodes of the amplifiers in the radio receiver.` The control grids are maintained at such a value as to prevent reception of signals in the receiver.

Although for purposes of illustration I have shown the at present preferred form of my invention it must be understood that I am not to be limited by the descriptions/as set forth in the foregoing specification but only by what appears in the appended claims:

I claim: l

1. In signalling apparatus a transmitter including a thermionic oscillation generator, a low frequency thermionic modulation frequency amplifier having its anode connected to an electrode in said oscillation generator, means for impressing voice frequency between the input electrodes of said modulation frequency amplifier, a biasing resistance connected between the input electrodes of said modulation frequency amplifier, a radio receiver including thermionic tubes, means for applying a normal biasing potential to the control electrodes of the thermionic tubes in said receiver and means for altering the potential applied to the control electrodes of said tubes including a connection between the control grids of the tubes in the radio receiver and the biasing resistance in the modulation frequency amplifier in the transmitter.

2. A duplex signalling station comprising a transmitting aerial, a thermionic oscillation generator connected therewith, a voice frequency amplifier connected with said thermionic oscillation generator, a receiving aerial, a thermionic receiver including a plurality of casoaded amplifier stages connected with said receiving aerial,

a resistance connected in series with the direct current input circuit of said Voice frequency amplifler, for utilizing the potential drop in said resistance when the direct current components of voice frequencies flow therein to increase the amplification factor of said amplifier and render said oscillation generator operative when signal currents fioW in said input circuit and a connection between said resistance and said receiver amplifier'stages for rendering said receiver inoperative when signal currents flow in said input circuit.

3. A signalling station comprising a transmitter including a thermionic oscillation generator having coupled anode and control electrodes and an auxiliary electrode, a modulation frequency amplifier tube having its anode electrode connected with the auxiliary electrode of said thermionic oscillation generator to control the potential thereof, a modulation frequency responsive device connected in series with a resistance in the input circuit of said modulation frequency amplifier, a thermionic receiver including a plurality of cascaded amplifier stages having input and output circuits, and means comprising a connection between the resistance in the input circuit of said modulation frequency amplifier and the input cir- .1513

VKtio cuits of said Aamplifier stages for rendering said receiver inoperative when said modulation frequency responsive device is energized and currents 110W in said inputcircuit.

4. Asignalling station `comprising a transmitting aerial, an oscillation generator ofthe -thermionic Vtube type having its output electrode coupled With saidaerial, a signal 'frequency amplifier having input and output electrodes vand input and output circuits, signalling means in series with aresistance inthe input circuit of said signal frequency amplier, means connected with the output circuit of said amplifier for determining the conductivity of said oscillation generator, a receiving aerial, a thermionic receiver including a plurality of cascaded amplier stages having input and-output circuits, and a connection between the input-circuit of one or more of said last named amplier stages and the resistance in the input circuit of `said signal frequency amplifier.

5. A signalling system comprising, a thermionic tube-having high frequency input and output circuits in which oscillations to be modulated appear, a signal frequency thermionic amplifier connected With said tube and circuits for Vmodulating the oscillations in said circuit-s,-said tliermionic amplier uhavingenergizing circuits includinga direct current input circuit, a receiver including ther mionic signal vrepeating means, a resistance connected in said direct current inputv circuit of said signal frequency amplier, means for utilizingthe potential dropin said resistance when lcornponents cffsignall frequency 'flow therein "to render said iir's't named -tube-more leiii'cient when signal frequencies iioWin-said input circuit, and a connection between Asaid resistance and said thermionic repeating means in .-'said 'receiver fori-rendering said repeating means inoperative when signal currents 'fi'oW insaid input circuit o'f said amplifier.

6. In combination, a Vvconstant 'frequency generator including fa thermionic 'tube having input electrodes, output felectrodes yand an auxiliary electrode, said output electrodes being connected in an oscillation circuit, `sa`i`d 4input velectrodes being yconnected to a linear conductor, a terminal of which is capacitively coupled to said oscillation circuit, said conductor being of a length to insure oscillations in said oscillation circuit of the desired frequency, a thermionic modulation frequency amplifier having `input and output electrodes, a source of modulating frequencyconnected with said input electrodes, and a circuit between said output electrode of Vsaid modulation frequency amplifier and said auxiliary electrode insaid iirst named thermionic tube for rendering said generator operative When 'the input of `said modulation frequency amplifier is energized by modulating frequencies and vice versa.

'CLARENCE WESTON -HANsELn 

